人工养殖白鹇产卵习性和卵的变化

人工养殖白鹇产卵习性和卵的变化高育仁,曹丰质,姚伟兰（华南濒危动物研究所,广州５１０２６０）Ｖａｒｉａｔｉｏｎｓｉｎｅｇｇ－ｌａｙｉｎｇｈａｂｉｔａｎｄｅｇｇｓｉｚｅｏｆａｒｔｉｆｉｃｉａｌｌｙｂｒｅｅｄｉｎｇｓｉｌｖｅｒｐｈｅａｓａｎｔ￥．ＧａｏＹ...     

Variation in the ovocalyxin-32 gene in commercial egg-laying chickens and its relationship with egg production and egg quality traits

Avian eggshell quality is an important trait for commercial egg production, as the eggshell is the primary packaging material and antimicrobial barrier for the internal food resource. Strong eggshells are essential to ensure that eggs can reach their final destination without damage. Ovocalyxin-32 (OCX32) is a matrix protein found within the outer layers of the eggshell and in the cuticle. Numerous reports in the literature have identified association between variants in the gene encoding this protein, OCX32, and various eggshell quality traits. Thus, OCX32 is a candidate gene for selection for eggshell traits in commercial poultry populations. Sequencing of exons 2-6 of the OCX32 gene in eight elite brown and white eggshell commercial egg-laying lines revealed 28 SNPs and one SNP/indel. Eighteen of these SNPs were predicted to alter the amino acid sequence of the protein. Clusters of SNPs in complete linkage disequilibrium were found in both exons 2 and 6. A total of 19 different versions or protein-sequence haplotypes of the OCX32 protein were inferred, revealing considerable variation within commercial lines. Genotypes for 13 of the SNPs were determined for 330-1819 individuals per line. Trait association studies revealed a significant effect of OCX32 on shell color in white egg lines and line-specific significant effects on albumen height, early egg weight, puncture score, and yolk weight. Three of the lines showed a significant change in OCX32 frequency over time, indicating selection pressure for certain variants of this gene during the breeding program.     

Vitellogenin and egg production in the moth,Heliothis virescens

The characteristics of vitellogenin (Vg) and the relationship between Vg production and egg production in the tobacco budworm, Heliothis virescens, were studied. The relationship between Vg production and juvenile hormone (JH) and the impact of mating on Vg and egg production were also investigated. Vg appears in the hemolymph of H. virescens about 6 h after moth eclosion. Vg may be separated into two apoproteins (ApoVg-I and ApoVg-II) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weights were calculated to be 156,065 ± 800 for ApoVg-I and 39,887 ± 323 for ApoVg-II. SDS-PAGE analysis revealed that the female hemolymph Vg polypeptides appear to be identical to those from eggs but are absent in male hemolymph. Vg concentration was significantly higher in mated females than in virgin females of the same age at 48 h after emergence. Rates of egg production increased as Vg production increased; rates of egg production in mated females were significantly higher than those of virgin females at 48, 72, 96, and 120 h postemergence. Vg production is dependent on JH, because hemolymph from decapitated females lacked Vg while that of decapitated females treated with synthetic JH had Vg at levels comparable to similarly aged, normal H. virescens females. Hemolymph JH titers in mated females were significantly higher compared with those in virgin females at all sampling periods. The high JH level in mated females may explain the high Vg and egg production in mated H. virescens. Arch. Insect Biochem. Physiol. 34:287–300, 1997. © 1997 Wiley-Liss, Inc.     

Widespread reproductive variation in North American turtles: temperature, egg size and optimality

Theory predicts the existence of an optimal offspring size that balances the trade-off between offspring fitness and offspring number. However, in wild populations of many species, egg size can still vary from year to year for unknown reasons. Here, we hypothesize that among-year variation in population mean egg size of freshwater turtles is partly a consequence of their gonadal sensitivity to seasonal temperatures, a physiological mechanism which principally functions to synchronize reproduction with a favorable time of year. As part of this process, among-year variation in seasonal temperatures modifies the extent of egg follicle development, and this may translate into variation in mean egg size among years (both at the individual and population level). To test this hypothesis, we applied an information-theoretic approach to model relationships between mean egg mass and the temperatures experienced during discrete periods of follicular development in wild populations of three turtle species (Chrysemys picta, Chelydra serpentina, Glyptemys insculpta) over 12 consecutive years. Because follicular development occurs in the fall for C. serpentina and G. insculpta, whereas it occurs both in the fall and spring for C. picta, we expected only fall temperatures would explain egg size variation in C. serpentina and G. insculpta, whereas both fall and spring temperatures would correlate with egg size variation in C. picta. These predictions were upheld. We then compared among-year variation in within-female egg and clutch sizes of each species in order to evaluate whether such variation might still be consistent with some tenets of optimal egg size theory. In all three species, we found that clutch sizes vary more than egg sizes in spite of temperature-induced egg size variation, and this pattern of relatively high clutch-size variation matches theoretical predictions. Future work should explore the roles of direct and indirect (i.e., nutritional) influences of temperature on egg size in natural settings.     

Avian egg size: variation within species and inflexibility within individuals

Egg size is a widely-studied trait and yet the causes and consequences of variation in this trait remain poorly understood. Egg size varies greatly within many avian species, with the largest egg in a population generally being at least 50% bigger, and sometimes twice as large, as the smallest. Generally, approximately 70% of the variation in egg mass is due to variation between rather than within clutches, although there are some cases of extreme intra-clutch egg-size variation. Despite the large amount of variation in egg size between females, this trait is highly consistent within individuals between breeding attempts; the repeatability of egg size is generally above 0.6 and tends to be higher than that of clutch size or laying date. Heritability estimates also tend to be much higher for egg size (> 0.5) than for clutch size or laying date (< 0.5). As expected, given the high repeatability and heritability of egg size, supplemental food had no statistically significant effect on this trait in 18 out of 28 (64%) studies. Where dietary supplements do increase egg size, the effect is never more than 13% of the control values and is generally much less. Similarly, ambient temperature during egg formation generally explains less than 15% of the variation in egg size. In short, egg size appears to be a characteristic of individual females, and yet the traits of a female that determine egg size are not clear. Although egg size often increases with female age (17 out of 37 studies), the change in egg size is generally less than 10%. Female mass and size rarely explain more than 20% of the variation in egg size within species. A female's egg size is not consistently related to other aspects of reproductive performance such as clutch size, laying date, or the pair's ability to rear young. Physiological characteristics of the female (e.g. endogenous protein stores, oviduct mass, rate of protein uptake by ovarian follicles) show more promise as potential determinants of egg size. With regards to the consequences of egg-size variation for offspring fitness, egg size is often correlated with offspring mass and size within the first week after hatching, but the evidence for more long-lasting effects on chick growth and survival is equivocal. In other oviparous vertebrates, the magnitude of egg-size variation within populations is often as great or greater than that observed within avian populations. Although there are much fewer estimates of the repeatability of egg size in other taxa, the available evidence suggests that egg size may be more flexible within individuals. Furthermore, in non-avian species (particularly fish and turtles), it is more common for female mass or size to explain a substantial proportion of the variation in egg size. Further research into the physiological basis of egg-size variation is needed to shed light on both the proximate and ultimate causes of intraspecific variation in this trait in birds.     

The relationship between female body size and egg size in pipefishes

Comparing five species of pipefish, egg size was significantly larger in species with brood pouches (Syngnathus typhle, Syngnathus acus and Syngnathus rostellatus) than in species without brood pouches (Entelurus aequoreus and Nerophis ophidion). Egg size correlated positively with female body size in species with brood pouches, but was similar across female sizes in the species lacking pouches. These results may reflect differences in offspring competition as a consequence of variable offspring relatedness within a brood, due to the mating systems adopted by the different species and the presence or absence of a brood pouch.     

Clutch size, intraclutch egg size variation, and breeding strategy in the GoldcrestRegulus regulus

Summary In Fennoscandia the Goldcrest regularly lays two clutches per breeding season. Near Trondheim in Central Norway (about 63° N) the mean size of 11 first clutches was 10.4 (9–12) eggs and of 10 second/repeat clutches 9.4 (8–11) eggs. Mean egg length was 13.49 mm, breadth 10.35 mm, mean weight of freshly-laid eggs 0.78 g, volume 737 mm³ and shape index 130.6. The correlation coefficient for egg length against weight was 0.47, and for egg breadth against weight 0.77. For the four clutches studied in more detail, all egg dimensions, except the shape index, increased with the laying sequence. On average, the last-laid egg was 20.1 % heavier than the first-laid egg, or 5.6 % heavier than the mean weight for the whole clutch. The 3–5 last-laid eggs in the clutch deviated by about the same magnitude from the clutch mean. Because of the pronounced asynchrony in hatching, the size-hierarchy within a Goldcrest brood may be considerable, at least 1:5. The survival chances of the smallest young in a brood apparently depend mainly on the prevailing food supply. The primary advantage of hatching from a relatively large-sized egg is probably that such a hatchling is strong enough to secure itself a favourable feeding position in the crowded nest, in which the young often form 2–3 horizontal layers. The parental selection of food is adjusted to the size of the young, even in a brood with a marked size-hierarchy. It is concluded that the Goldcrest has evolved a brood reduction strategy.

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Gelegegröße, Variation der Eigröße und Brutstrategie beim Wintergoldhähnchen (Regulus regulus)

Zusammenfassung In Fennoskandien zeitigt das Wintergoldhähnchen regelmäßig zwei Gelege pro Brutsaison. In einem Kontrollgebiet bei Trondheim in Mittelnorwegen (ca. 63° N) betrug die mittlere Gelegegröße für 11 Erstgelege 10,4 (9–12) und für 10 Zweit- bzw. Ersatzgelege 9,4 (8–11) Eier. Die mittlere Eilänge betrug 13,5 mm, die Eibreite 10,35 mm, das mittlere Frischvollgewicht 0,78 g; das Volumen maß 737 mm³, der Eiformindex (=Länge/Breite × 100) 130,6. Die Korrelation zwischen Länge und Gewicht betrug 0,47, zwischen Breite und Gewicht 0,77. Bei vier genauer untersuchten Gelegen nahmen alle Eidimensionen mit Ausnahme des Eiformindex mit der Legefolge zu. Im Mittel war das letzte Ei 20,1 % schwerer als das erste oder 5,6 % schwerer als das mittlere Gewicht des gesamten Geleges; letzteres gilt auch für die 3 bis 5 zuletzt gelegten Eier. Als Folge des bemerkenswert asynchronen Schlupfes sind die Größenunterschiede innerhalb einer Goldhähnchenbrut beachtlich, nämlich mindestens 1:5. Die Überlebenschancen des kleinsten Jungen einer Brut hängen offensichtlich vor allem vom Nahrungsangebot ab. Der primäre Vorteil eines Jungen aus einem großen Ei liegt möglicherweise darin, daß dieser Nestling stark genug ist, um sich eine günstige Position im dichtbesetzten Nest bei den Fütterungen zu sichern. Die Jungen liegen oft in zwei bis drei Schichten übereinander. Die Nahrungswahl der Altvögel richtet sich nach der Jungengröße, sogar in einer Brut mit deutlichen Größenunterschieden. Das Wintergoldhähnchen hat wahrscheinlich die Strategie einer Brutreduzierung in Anpassung an knappes Nahrungsangebot entwickelt.

     

Ovarian dynamics, egg size, and egg number in relation to temperature and mating status in a butterfly

Although the temperature‐size rule, that is, an increase in egg (and body) size at lower temperatures, applies almost universally to ectotherms, the developmental mechanisms underlying this consistent pattern of phenotypic plasticity are hitherto unknown. By investigating ovarian dynamics and reproductive output in the tropical butterfly Bicyclus anynana (Butler) (Lepidoptera: Nymphalidae: Satyrinae) in relation to oviposition temperature and mating status, we tested the relevance of several competing hypotheses for temperature‐mediated variation in egg size and number. As expected, females ovipositing at a lower temperature laid fewer but larger eggs than those ovipositing at a higher temperature. Despite pronounced differences in egg‐laying rates, oocyte numbers were equal across temperatures at any given time, while oocyte size increased at the lower temperature. In contrast, there were greatly reduced oocyte numbers in mated compared to virgin females. Our results indicated that temperature‐mediated plasticity in egg size cannot be explained by reduced costs of somatic maintenance at lower temperatures, enabling the allocation of more resources to reproduction (reproductive investment was higher at the higher temperature). Furthermore, there was no indication for delayed oviposition (no accumulation of oocytes at the lower temperature, in contrast to virgin females). Rather, low temperatures greatly reduced the oocyte production (i.e., differentiation) rate and prolonged egg‐maturation time, causing low egg‐laying rates. Our data thus suggested that oocyte growth is less sensitive to temperature than oocyte production, resulting in a lower number of larger eggs at lower temperatures.     

Adrenocortical responses in zebra finches (Taeniopygia guttata): individual variation, repeatability, and relationship to phenotypic quality

Although individual variation is a key requirement for natural selection, little is known about the magnitude and patterns of individual variation in endocrine systems or the functional significance of that variation. Here we describe (1) the extent and repeatability of inter-individual variation in adrenocortical responses and (2) its relationship to sex-specific phenotypic quality, such as song duration and frequency and timing of egg laying. We measured adrenocortical responses to a standardized stressor in zebra finches (Taeniopygia guttata) at two life history stages: approximately day 16 (nestlings) and 3 months of age (sexually mature adults). Subsequently, we assessed phenotypic (reproductive) quality of all individuals as adults. Marked inter-individual variation in the adrenocortical response was seen in both sexes and ages, e.g., stress-induced corticosterone ranged from 2.2 to 62.5 ng/mL in nestlings and 5.0-64.0 ng/mL in adults. We found sex differences in (a) inter-individual variation in the adrenocortical response, (b) repeatability, and (c) relationships between corticosterone levels and phenotypic quality. In males, variation in nestling corticosterone was weakly but positively correlated with brood size and negatively correlated with nestling mass (though this relationship was dependent on one individual). There was no significant correlation of adrenocortical responses between two stages in males and adult phenotypic quality was significantly correlated only with adult corticosterone levels. In contrast, in females there was no relationship between nestling corticosterone and brood size or mass but adrenocortical response was repeatable between two stages (r2=0.413). Phenotypic quality of adult females was correlated with nestling baseline and adrenocortical response.     

Spatial variation in egg size and egg number reflects trade-offs and bet-hedging in a freshwater fish

1.?Maternal reproductive investment is thought to reflect a trade-off between offspring size and fecundity, and models generally predict that mothers inhabiting adverse environments will produce fewer, larger offspring. More recently, the importance of environmental unpredictability in influencing maternal investment has been considered, with some models predicting that mothers should adopt a diversified bet-hedging strategy whilst others a conservative bet-hedging strategy. 2.?We explore spatial egg size and fecundity patterns in the freshwater fish southern pygmy perch (Nannoperca australis) that inhabits a diversity of streams along gradients of environmental quality, variability and predictability. 3.?Contrary to some predictions, N.?australis populations inhabiting increasingly harsh streams produced more numerous and smaller eggs. Furthermore, within-female egg size variability increased as environments became more unpredictable. 4.?We argue that in harsh environments or those prone to physical disturbance, sources of mortality are size independent with offspring size having only a minor influence on offspring fitness. Instead, maternal fitness is maximized by producing many small eggs, increasing the likelihood that some offspring will disperse to permanent water. We also provide empirical support for diversified bet-hedging as an adaptive strategy when future environmental quality is uncertain and suggest egg size may be a more appropriate fitness measure in stable environments characterized by size-dependent fitness. These results likely reflect spatial patterns of adaptive plasticity and bet-hedging in response to both predictable and unpredictable environmental variance and highlight the importance of considering both trait averages and variance. 5.?Reproductive life-history traits can vary predictably along environmental gradients. Human activity, such as the hydrological modification of natural flow regimes, alters the form and magnitude of these gradients, and this can have both ecological and evolutionary implications for biota adapted to now non-existent natural environmental heterogeneity.     

Comparative fecundity, clutch size, ovariole number and egg size of Dacus tryoni and D. jarvisi, and their relationship to body size

Dacus tryoni (Frogg.) (Diptera: Tephritidae) is the main tephritid pest of cultivated fruits in Australia. D. jarvisi (Tryon) is also able to infest these fruits. Some factors influencing the rate at which D. tryoni and D. jarvisi exploit patches of host fruits were examined to determine whether one species may have an advantage when they exploit the same fruits in the field. Measurements of the intrinsic rate of increase, ovariole number, clutch size and egg size and the influence of body size on these parameters were made for both species in the laboratory. Up to 10 weeks of age D. tryoni produced twice as many eggs as D. jarvisi, most during a peak 3–5 weeks after adult emergence. The difference in fecundity up to 10 weeks can be explained partly by the higher number of ovarioles in D. tryoni (38/ovary) compared to D. jarvisi (27/ovary). In addition D. tryoni produces smaller eggs than D. jarvisi and distributes them in smaller clutches; 3–4 eggs/clutch vs 10–15. In both species there was a positive correlation between ovariole number and body size (as measured by wing length). By contrast, egg size remained constant over a broad range of body sizes. The influence of these life history differences on the interaction between D. tryoni and D. jarvisi in the field is discussed.

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Résumé D. tryoni Frogg est la principale téphrididae nuisible aux fruits cultivés en Australie. Cependant, plusieurs autres espèces de Dacus, dont D. jarvisi Tryon sont susceptibles de contaminer ces fruits. Quelques facteurs influant sur le taux de contamination de fruits ont été examinés pour déterminer si une espèce peut être avantagée lors de l'exploitation des mêmes fruits dans la nature. L'influence de la taille de l'adulte sur le taux d'accroissement intrinsèque, sur le nombre d'ovarioles, sur l'effectif des pontes et sur la taille des ufs a été examinée au laboratoire sur les 2 espèces. Pendant les 10 premières semaines, D. tryoni produit 2 fois plus d'ufs que D. jarvisi, la plupart étant pondus entre la 3^e et la 5^e semaines après l'émergence. La production de D. tryoni diminue rapidement après ce maximum. D. jarvisi ne présente pas ce maximum précoce, et la production des ufs se fait au même rythme entre les 3^e et 7^e semaines, avant de diminuer graduellement. La différence de fécondité au bout de 10 semaines peut être expliquée partiellement par le plus grand nombre d'ovarioles de D. tryoni (38/ovaire) contre 24/ovaire pour D. jarvisi. De plus, D. tryoni forme des ufs plus petits que D. jarvisi et l'effectif de chacune de ses pontes est plus limité: 3 à 4 ufs contre 10 à 15. Chez les deux espèces, il y a une relation directe nette entre le nombre d'ovarioles et la taille du corps de la femelle (mesurée par la longueur de l'aile). Par contre, la taille des ufs est indépendante d'une grande gamme de tailles du corps des femelles. Les caractéristiques biologiques de D. tryoni le rendent capable de contaminer rapidement les bouquets de fruits qu'il vient de coloniser, ce qui réduit les disponibilités pour les autres espèces susceptibles de contaminer ces fruits. Dans le cas particulier de D. jarvisi, D. tryoni a peu d'impact sur son niveau de population, puisque D. jarvisi peut exploiter aussi son hôte d'origine, Planchonia careya: Il ne tend à entrer en compétition avec D. tryoni que pour une ou deux générations tardives en été, quand l'hôte partage (la goyave) est souvent abondant. Néanmoins, si les fruits sont rares à cette époque ou si les 2 espèces sont obligées de partager leurs hôtes pendant plusieurs générations (hors de l'aire de Planchonia), D. tryoni aura un avantage certain.

     

Sibling-size variation in brown trout Salmo trutta in relation to egg size and stream size

Sibling-size variation (SSV), estimated as the coefficient of variation of egg size, was investigated for 13 populations of brown trout Salmo trutta . SSV was negatively correlated with mean egg size both at the population and individual levels. After correction for the effect of mean egg size, SSV was also negatively correlated with stream size. These results provide new information about how salmonid SSV can vary at different ecological scales (individual, population and region). The results are discussed in light of competing theories for explaining SSV: (1) the passive effect hypothesis, stating that egg size variation follows passively from selection on egg size and (2) the bet-hedging hypothesis, stating that high SSV is adaptive in unpredictable environments.     

Annual variation in the seasonal shift in egg size and clutch size in Sceloporus woodi

Summary Early and late season clutch parameters were examined over a three year period in the Florida scrub lizard, Sceloporus woodi. Precipitation levels were monitored throughout the study. In the early and late season of 1984 and the early season of 1986 precipitation levels approximated long-term mean levels of precipitation. In 1985 a severe winter drought occurred. Clutch size was positively related to body size in all samples in every year. In 1984 and 1986, egg size was not related to clutch size, whereas, in 1985 egg size was negatively related to clutch size. In 1985, females produced large clutches of small eggs early in the season and small clutches of large eggs late in the season. In 1984, no seasonal changes in egg or clutch size occurred. In the late season of 1986, females produced the largest clutches and the smallest eggs of all the samples, but egg and clutch size were not statistically different from the early season egg and clutch size of 1986. Total clutch dry weight, an estimate of total clutch energy, was not different in any of the six sampling periods. These data do not support current adaptationist models that attempt to explain the control of clutch and egg size in lizards. It is argued in this paper that egg and clutch size may vary in response to past environments that affect a female's physical condition, as well as, current resources that may be important for maintenance and reproduction. Egg and clutch size appear to be plastic traits selected to respond to proximal environmental variation, whereas, the investment of total dry matter/clutch has been optimized.     

Latitudinal variation in body size of Agrilus planipennis and relationship with fecundity

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Landscape-mediated variation in diet is associated with egg size and maculation in a generalist forager

Human impacts alter landscapes with consequences for the distribution and availability of high-quality food resources to populations inhabiting those landscapes, which may impact on the reproductive output of individuals in those populations. The sensitivity of wild populations to changes in food resources may vary among stages of the annual cycle. For example, in birds, effects are likely to be greater during costly stages such as egg production. Here we compare assimilated diet (from stable isotope analysis of chick feathers) and egg traits (egg size, shape, eggshell colour and maculation, using pattern-analysis software) in Herring Gulls Larus argentatus, across seven colonies in southwest Scotland and Northern Ireland. The Herring Gull is an opportunistic, generalist forager on both marine and terrestrial resources which frequently exploits anthropogenic food sources such as fishery discards and human refuse. We found that larger eggs were laid in colonies where females consumed either a higher proportion of marine resources or terrestrial resources; smaller eggs were laid in colonies where females had an intermediate diet. In colonies where females consumed more marine items, they also laid eggs with higher maculation (intensity and size of spots) compared with colonies where females mainly consumed terrestrial food. We also found smaller and more pointed eggs, suggestive of resource shortages, in larger colonies. Generalist foragers are often thought to have the capacity to buffer themselves against changes in the food web, provided that enough alternative food is available. However, this study highlights that specializing on the most profitable or available resources has consequences for egg traits even in an opportunistic generalist forager exploiting a large range of habitats. If variation in egg traits is related to reproductive output, then understanding the impact of assimilated diet on reproduction early in the breeding season can provide important insights into how populations will respond to landscapes altered by human impact.     

Seasonal variation of egg size and number in a Daphnia pulex population

Seasonal variation of egg size and number was examined in a Daphnia pulex population inhabiting a vernal pond. In this population, size at maturity declines at midseason, probably as an adaptive response to size-selective predation by larvae of the salamander Ambystoma. The larger early season individuals produce more and larger eggs than the smaller late season individuals. Age at maturity does not vary between seasons. Laboratory experiments indicate that temperature may affect egg size, egg number and size at maturity. However, field data suggest that temperature accounts for only a small fraction of the total variation in egg size and number. Indirect measures of nutrition indicate that food limitation does not cause the seasonal decline in egg size and number. The seasonal change in reproductive traits is well correlated with changes in invertebrate and vertebrate predation. Examination of predator feeding preferences and their impact on Daphnia mortality indicate that variation of reproductive traits is most likely a complex adaptation to changing predation regimes.     

Eye size variation reflects habitat and daily activity patterns in colubrid snakes

The functioning of the vertebrate eye depends on its absolute size, which is presumably adapted to specific needs. Eye size variation in lidless and spectacled colubrid snakes was investigated, including 839 specimens belonging to 49 genera, 66 species and subspecies. Variations of adult eye diameters (EDs) in both absolute and relative terms between species were correlated with parameters reflecting behavioral ecology. In absolute terms, eye of arboreal species was larger than in terrestrial and semiaquatic species. For diurnal species, EDs of terrestrial species do not differ from semiaquatic species; for nocturnal species the ED of terrestrial species is larger than fossorial species but not different from semiaquatic species. In relative terms, ED did not differ significantly by habitat for diurnal species. Although the ED of terrestrial species is larger than fossorial species there were no differences for nocturnal species between semiaquatic and fossorial snakes. In contrast to other vertebrates studied to date, colubrid EDs in absolute and relative terms are larger in diurnal than in nocturnal species. These observations suggest that among colubrid snakes, eye size variation reflects adaptation to specific habitats, foraging strategies and daily activities, independently of phylogeny. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

How avian incubation behaviour influences egg surface temperatures: relationships with egg position,development and clutch size

While understanding heat exchange between incubating adults and their eggs is central to the study of avian incubation energetics, current theory based on thermal measurements from dummy eggs reveals little about the mechanisms of this heat exchange or behavioural implications for the incubating bird. For example, we know little about how birds distribute their eggs based on temperature differences among egg positions within the nest cup. We studied the great tit Parus major, a species with a large clutch size, to investigate surface cooling rates of individual eggs within the nest cup across a range of ambient temperatures in a field situation. Using state‐of‐the‐art portable infrared imaging and digital photography we tested for associations between egg surface temperature (and rate of cooling) and a combination of egg specific (mass, shape, laying order, position within clutch) and incubation specific (clutch size, ambient temperature, day of incubation) variables. Egg surface temperature and cooling rates were related to the position of the eggs within the nest cup, with outer eggs being initially colder and cooling quicker than central eggs. Between foraging bouts, females moved outer eggs significantly more than centrally positioned eggs. Our results demonstrate that females are capable of responding to individual egg temperature by moving eggs around the nest cup, and that the energy cost to the female may increase as incubation proceeds. In addition, our results showing that smaller clutches experience lower initial incubation temperatures and cool quicker than larger clutches warrant further attention for optimal clutch size theory and studies of energetic constraints during incubation. Finally, researchers using dummy eggs to record egg temperature have ignored important elements of contact‐incubation, namely the complexity of how eggs cool and how females respond to these changes.     

Environmental,parental and adaptive variation in egg size of Tengmalm's owls under fluctuating food conditions

We studied egg size variation of Tengmalm's owls in western Finland during 1981–1990. The owls fed on voles whose population fluctuated in a predictable manner: low (1981, 1984, 1987, 1990), increase (1982, 1985, 1988) and peak (1983, 1986, 1986) phases of the cycle occurred every third year. Eggs were largest in the increase phase of the vole cycle, even though that voles were more abundant and egg-laying started earlier in the peak phase than in the increase phase. This suggests that owls invest mostly in egg size when vole abundance increases along with survival chances of offspring. Territory quality and female age had no effects on egg size, but egg size decreased with laying data in the increase phase of the vole cycle. Egg size was significantly positively related to the male age in the increase phase, but the opposite relationship was significant in the peak phase of the vole cycle. The partners of adult males also decreased their egg volume from the increase to the peak phase, whereas the partners of yearling males produced their largest eggs in the peak phase of the vole cycle. This suggests the importance of experience in prevailing food fluctuations. Possibly male Tengmalm's owls can adjust the intensity of courtship feeding not only in relation to the food abundance on their territories at the time of egg laying, but also to the survival prospects of their offspring. Phenotypic plasticity seems to play a substantial role, as the egg size repeatabilities of individual females and partners of individual males were low. Obviously, under cyclic food conditions, predictability and inter-generational trade-offs are important to life history traits.